Transcription factor (RIPE3b1) binding to the insulin gene enhancer element RIPE3b (A2-C1) is selectively expressed in pancreatic beta cells, and plays an important role in regulating beta cell specific expression of the insulin gene. In addition, the RIPE3b1 factor is a major glucose responsive transcriptional regulator of beta-cell function. Transcription factors BETA2 and PDX-1 are also important for regulating beta cell specific and glucose responsive expression of the insulin gene. Additionally, PDX-1 and BETA2, play a major role in pancreatic development and differentiation of beta cells. Hence, we hypothesize that the RIPE3b1 factor will be a major regulator of pancreatic beta cell function and pancreatic development. Using a combination of biochemical purification, amino acid sequence determination, we have successfully identified and cloned the RIPE3b1 factor as a novel mammalian homologue of the avian MafA/L-Maf factor (mMafA). Avian homologue of RIPE3b1 is an important differentiation factor that is 1) highly restricted in its expression, 2) can induce expression of several genes, and 3) when expressed ectopically induce differentiation. This is consistent with our hypothesis for a role of RIPE3b1 factor in regulating function, development and differentiation of pancreatic beta cells. Furthermore, we show that the RIPE3b1 gene is expressed only in pancreatic beta cells and not in alpha cells, supporting role of this factor in differentiation of beta cells. Hence, we propose to perform targeted ablation of the gene in mice to determine the role of the RIPE3b1 activator in pancreatic development. When expressed as a transgene, we will determine the ability of this factor to induce insulin gene expression in non-insulin producing cells, and to characterize the mechanisms by which the RIPE3b1 activator regulates insulin expression. Results from these studies will be instrumental in developing new strategies for beta cell replacement as a treatment for diabetes. [unreadable] [unreadable]